Absorbent articles for absorption of body fluids such as menses or blood are well known in the art, and comprise for example feminine hygiene articles such as sanitary napkins, panty liners, tampons, interlabial devices, as well as wound dressings, and the like. When considering for example sanitary napkins, these articles typically comprise a liquid-pervious topsheet as wearer-facing layer, a backsheet as garment-facing layer and an absorbent core between topsheet and backsheet. The body fluids are acquired through the topsheet and subsequently stored in the absorbent core. The backsheet typically prevents the absorbed fluids from wetting the wearer's garment.
An absorbent core can typically comprise one or more fibrous absorbent material, which in turn can comprise natural fibers, such as for example cellulose fibers, typically wood pulp fibers, synthetic fibers, or combinations thereof.
Absorbent articles can further comprise, typically in the absorbent core, superabsorbent materials, such as absorbent gelling materials (AGM), usually in finely dispersed form, e.g. typically in particulate form, in order to improve their absorption and retention characteristics. Superabsorbent materials for use in absorbent articles typically comprise water-insoluble, water-swellable, hydrogel-forming crosslinked absorbent polymers which are capable of absorbing large quantities of liquids and of retaining such absorbed liquids under moderate pressure. Absorbent gelling materials can be incorporated in absorbent articles, typically in the core structure, in different ways; for example, absorbent gelling materials in particulate form can be dispersed among the fibers of fibrous layers comprised in the core, or rather localized in a more concentrated arrangement between fibrous layers.
Absorbent cores for absorbent articles having a thin structure can further provide an improved immobilization of absorbent gelling materials, particularly when the article is fully or partially loaded with liquid, and an increased wearing comfort. Such thinner structures provide absorbent articles combining better comfort, discreetness and adaptability, such as for example, thin absorbent structures where the absorbent gelling material is located and somehow kept in selected, e.g. patterned regions of the structure itself.
EP 724418 (Tanzer) for example, discloses an absorbent article which includes superabsorbent material located in discrete pockets. The absorbent article comprises a first and a second carrier layer and water-sensitive attaching means for securing together the carrier layers and to provide a plurality of pocket regions. The article comprises high-absorbency material located within said pocket regions. The water-sensitive attachment means provides a wet strength which is less than a separating force imparted by a swelling of that high-absorbency material when that high-absorbency material is exposed to an aqueous liquid. The absorbent article is said to provide an absorbent structure which more securely locates and contains the high-absorbency material in said pockets when the article is dry. However, due to the construction of the pockets, it is believed that this absorbent article does not provide a very satisfactory immobilization of the absorbent material in the fully or partially urine loaded state.
EP 1447067, assigned to the Procter & Gamble Company, describes an absorbent article, typically a disposable absorbent article, such as a diaper, having an absorbent core which imparts increased wearing comfort to the article and makes it thin and dry. The absorbent core comprises a substrate layer, the substrate layer comprising a first surface and a second surface, the absorbent core further comprising a discontinuous layer of absorbent material, the absorbent material comprising an absorbent polymer material, the absorbent material optionally comprising an absorbent fibrous material which does not represent more than 20 weight percent of the total weight of the absorbent polymer material. The discontinuous layer of absorbent material comprises a first surface and a second surface, the absorbent core further comprising a layer of thermoplastic material, the layer of thermoplastic material comprising a first surface and a second surface and wherein the second surface of the discontinuous layer of absorbent material is in at least partial contact with the first surface of the substrate layer and wherein portions of the second surface of the layer of thermoplastic material are in direct contact with the first surface of the substrate layer and portions of the second surface of the layer of thermoplastic material are in direct contact with the first surface of the discontinuous layer of absorbent material.
While absorbent articles according to EP 1447067 and comprising thin absorbent cores with relatively high amounts of absorbent gelling materials and rather low content of fibrous materials commonly have good absorption and retention characteristics to body fluids like urine, there still remains room for improvement of absorption and retention towards other body fluids. In particular, menses and blood are particularly difficult to be effectively absorbed and retained into absorbent cores containing superabsorbent materials in major amounts since such materials do not show optimal absorption and retention characteristics towards such body fluids.
It is believed that the non-optimal absorption and retention are mainly caused by poor permeability of superabsorbent materials towards menses and blood due to the viscosity and/or to the complex nature of these fluids. Menses and blood are water based fluids comprising components having molecular weights higher than water and also corpuscular components, including red cells, white cells, soluble proteins, cellular debris and mucus, which slow down the absorption of these fluids by superabsorbents. Menses and blood are rather thick, and more difficult to absorb in conventional absorbent structures comprising absorbent gelling materials; moreover, corpuscular components like red cells may decrease the absorption capacity of certain superabsorbent particles. This translates into a slower initial uptake rate of the fluid into the superabsorbent material, and in turn in the absorbent structure comprising the superabsorbent material, which can result in a lower final absorption and retention capacity.
Also when considering more in general fibrous absorbent materials, different fibers and different fibrous structures may show different behaviors and effectiveness towards various body fluids, particularly towards menses and blood. For example, cellulose fibers, such as for example wood pulp fibers, show a greater absorption and diffusion capacity towards the water fraction of menses and blood, which may be very rapidly acquired and may be transported within the fibrous structure, far from the initial acquisition area, while the corpuscular and higher molecular weight components do not diffuse equally well, and may remain closer to the initial acquisition area. Such corpuscular and higher molecular weight components tend to travel preferentially in a direction perpendicular to the plane of the absorbent structure. Also, natural and synthetic fibrous materials can be more or less suitable to provide compact, or alternatively bulkier, absorbent structures to be employed in absorbent cores.
Hence, there is still the need for an improved, thin absorbent core structure for an absorbent article, particularly for absorption of menses or blood, which comprises the absorbent gelling material in a non uniform layer stably provided onto a substrate layer, and which takes advantage of the peculiarities of the different fibrous and non-fibrous absorbent materials in the absorption and management of these complex body fluids, achieving a better result in terms of fluid acquisition and distribution. Such a structure could also be stably thin, or in any case should not significantly change (for example increase) its thickness upon absorption throughout its normal use.